1. Field of the Invention
The present invention relates to a spin-valve thin film element in which an electric resistance varies with, for example, the magnetization vector in a pinned magnetic layer and the a magnetization vector in a free magnetic layer affected by an external magnetic field. Specifically, the present invention relates to a magnetoresistive element which allows a sensing current to effectively flow into a multilayer film, as well as a process for manufacturing the electromagnetic element.
2. Description of the Related Art
FIG. 14 is a sectional view of the structure of a conventional magnetoresistive element taken from an air bearing surface (ABS).
The magnetoresistive element shown in FIG. 14 is a spin-valve thin film element and detects a recording magnetic field from a recording medium such as a hard disk. The spin-valve thin film element is a type of giant magnetoresistive element utilizing a giant magnetoresistive effect. This type of element.
The spin-valve thin film element includes a multilayer film 9 comprising an underlayer 6, an antiferromagnetic layer 1, a pinned magnetic layer 2, a nonmagnetic layer 3, a free magnetic layer 4, and a protective layer 7 layered in this order from the bottom, and a pair of hard bias layers 5 and 5 formed on both sides of the multilayer film 9, and a pair of electrode layers 8 and 8 formed on the hard bias layers 5 and 5. The underlayer 6 and the protective layer 7 are each made of, for example, a Ta (tantalum) film. The width of a top surface of the multilayer film 9 defines a track width Tw.
Generally, the antiferromagnetic layer 1 is made of an Fexe2x80x94Mn (iron-manganese) alloy film or a Nixe2x80x94Mn (nickel-manganese) alloy film, the pinned magnetic layer 2 and the free magnetic layer 4 are each made of a Nixe2x80x94Fe (nickel-iron) alloy film, the nonmagnetic layer 3 is made of a Cu (copper) film, the hard bias layers 5 and 5 is made of a Coxe2x80x94Pt (cobalt-platinum) alloy film, and the electrode layers 8 and 8 are each made of a Cr (chromium) film.
As shown in FIG. 14, the magnetization vector in the pinned magnetic layer 2 is put into a single magnetic domain state in the Y direction (direction of a leakage magnetic field from a recording medium; height direction) through an exchange anisotropic magnetic field with the antiferromagnetic layer 1. In contrast, the magnetization vector in the free magnetic layer 4 is aligned in the X direction by the effect of a bias magnetic field from the hard bias layers 5 and 5.
Specifically, the magnetization vector in the pinned magnetic layer 2 is set so as to be orthogonal to the magnetization vector in the free magnetic layer 4.
In the spin-valve thin film element, the electrode layers 8 and 8 formed on the hard bias layers 5 and 5 supply a sensing current to the pinned magnetic layer 2, the nonmagnetic layer 3 and the free magnetic layer 4. The magnetic recording medium, such as a hard disk, moves in the Z direction. When a leakage magnetic field from the magnetic recording medium is applied to the free magnetic layer 4 in the Y direction, the magnetization vector in the free magnetic layer 4 varies from the X direction to the Y direction. The electrical resistance depends on the variation in the magnetization vector in the free magnetic layer 4 and the magnetization vector in the pinned magnetic layer 2 (this is called as xe2x80x9cmagnetoresistive effectxe2x80x9d), hence the leakage magnetic field from the magnetic recording medium is detected by the variation in the voltage due to the variation in the electrical resistance.
However, the conventional magnetoresistive element shown in FIG. 14 has the following problems.
The electrode layers 8 and 8 of the magnetoresistive element shown in FIG. 14 have a decreasing thickness as they approach to front end faces 8a and 8a which are in contact with the multilayer film 9. A sensing current at a constant level cannot be always significantly allowed to flow even to the front end faces 8a and 8a of the electrode layers 8 and 8, and the sensing current is shunted on the way, part of which flows into the hard bias layers 5 and 5, to thereby reduce a read output.
Accordingly, it is an object of the present invention to provide a magnetoresistive element free from the above problems, in which electrode layers have some thickness even in regions where the electrode layers are in contact with a multilayer film and thereby can allow a sensing current to flow into a multilayer film of the magnetoresistive element always at a constant level to improve the reproducing characteristics, as well as to provide a process for manufacturing the magnetoresistive element.
Specifically, the present invention provides, in an aspect, a magnetoresistive element which includes a multilayer film including an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer, the magnetization vector in the pinned magnetic layer is fixed by an exchange anisotropic magnetic field with the antiferromagnetic layer, and a free magnetic layer formed on the pinned magnetic layer through the interposition of a nonmagnetic layer; a pair of bias layers formed on both sides of the multilayer film and aligning the magnetization vector in the free magnetic layer to a direction crossing the magnetization vector of the pinned magnetic layer; and a pair of electrode layers formed on the bias layers and supplying a sensing current to the pinned magnetic layer, the nonmagnetic layer and the free magnetic layer. In this element, an insulating layer is formed on the multilayer film between the electrode layers, and the electrode layers formed on both sides of the multilayer film are in contact with the sides of the insulating layer directly or through the interposition of another layer.
According to the present invention, front end faces of the electrode layers on the multilayer film side are laminated so as to be along the sides of the insulating layer, and the electrode layers have a large thickness even in regions where the electrode layers are in contact with the multilayer film, owing to the thickness of the insulating layer. Accordingly, a sensing current can be allowed to flow in the multilayer film of the magnetoresistive element always at a constant level to thereby improve the reproducing characteristics.
Preferably, the multilayer film includes a lamination of the antiferromagnetic layer, the pinned magnetic layer, the nonmagnetic layer, and the free magnetic layer in this order from the bottom, and the antiferromagnetic layer extends toward the portions on both sides of each of the layers formed on the antiferromagnetic layer, and a pair of the bias layers and a pair of the electrode layers are laminated on the antiferromagnetic layer in the portions on both sides through the interposition of a metallic film.
The present invention provides, in another aspect, a magnetoresistive element which includes a multilayer film including a free magnetic layer, nonmagnetic layers formed on and under the free magnetic layer, pinned magnetic layers formed on one nonmagnetic layer and under the other nonmagnetic layer where magnetization vectors in the pinned magnetic layers are fixed, and antiferromagnetic layers formed on one pinned magnetic layer and under the other pinned magnetic layer; a pair of bias layers formed on both sides of the multilayer film and aligning the magnetization vector in the free magnetic layer in a direction crossing the magnetization vectors in the pinned magnetic layers; a pair of electrode layers formed on the bias layers and supplying a sensing current to the pinned magnetic layers, the nonmagnetic layers, and the free magnetic layer. In the magnetoresistive element, an insulating layer is formed on the multilayer film between the electrode layers, and the electrode layers formed on both sides of the multilayer film are in contact with sides of the insulating layer directly or through the interposition of another layer.
An antioxidant protective layer may be formed on a top surface of the multilayer film.
A surface of the protective layer or a surface of the multilayer film other than the protective layer may preferably form an angle of 60 degrees or more, and more preferably of 90 degrees or more with respect to front end faces of the electrode layers extending over a dead zone of the multilayer film. By this configuration, a sensing current can be surely allowed to flow even into the front end faces of the electrode layers always at a constant level.
Preferably, the free magnetic layer includes plural soft magnetic thin films which have different magnetic moments and are laminated with each other through the interposition of a nonmagnetic material layer, and the free magnetic layer is in a ferrimagnetic state where the magnetization vectors of a pair of the soft magnetic thin films adjacent to each other through the interposition of the nonmagnetic material layer are in parallel with and opposite to each other. By this configuration, equivalent advantages to the case where the thickness of the free magnetic layer is thinned can be obtained, and the magnetization of the free magnetic layer becomes apt to vary to thereby improve magnetic field detecting (sensing) sensitivity of the magnetoresistive element.
The magnitude of the magnetic moment of the soft magnetic thin film is represented as the product of the saturation magnetization (Ms) and the thickness (t) of the soft magnetic thin film.
When the free magnetic layer includes plural soft magnetic thin films which have different magnetic moments and are laminated with each other through the interposition of a nonmagnetic material layer, a magnetic interface between the multilayer film and the bias layer preferably overlays a side of only one soft magnetic thin film, of sides of the plural soft magnetic thin films constituting the free magnetic layer.
The bias layer has only to align the magnetization vector in one soft magnetic thin film, of the plural soft magnetic thin films constituting the free magnetic layer. When the magnetization vector in one soft magnetic thin film is aligned in a fixed direction, a soft magnetic thin film adjacent to the aforementioned soft magnetic thin film is put into a ferrimagnetic state in which the magnetization vectors in the two layers are in parallel with and opposite to each other, and ultimately, the magnetization vectors of all the soft magnetic thin films are aligned in parallel in the same or opposite direction, and hence the magnetization vector in the overall free magnetic layer is aligned in a fixed direction.
If the bias layer is magnetically connected with the plural soft magnetic thin films constituting the free magnetic layer, the magnetic orientations of such soft magnetic thin films, which are in the opposite direction to the orientation of a magnetic field produced from the bias layer, are disturbed in the vicinity of both side portions where the soft magnetic thin films are magnetically connected with the bias layer. In this case, the magnetization vectors of soft magnetic thin films in the vicinity of the both side portions, which orientations are oriented in a direction of a magnetic field produced from the bias layer, are also disturbed by the effect of the above disturbance.
In addition, the pinned magnetic layer preferably includes plural soft magnetic thin films having different magnetic moments and laminated with each other through the interposition of a nonmagnetic material layer, and the pinned magnetic layer is preferably in a ferrimagnetic state where the magnetization vectors in a pair of the soft magnetic thin films being adjacent to each other through the interposition of the nonmagnetic material layer are in parallel with and opposite to each other. By this configuration, the plural soft magnetic thin films constituting the pinned magnetic layer serve to fix the magnetization vectors of the other soft magnetic thin films to thereby stabilize the magnetization vector in the overall pinned magnetic layer in a fixed direction.
The magnitude of the magnetic moment of the soft magnetic thin film in this case is also represented by the product of the saturation magnetization (Ms) and the thickness (t) of the soft magnetic thin film.
The nonmagnetic material layer is preferably made of one metal or of an alloy of two or more metals selected from Ru, Rh, Ir, Cr, Re, and Cu.
In the invented magnetoresistive element, the antiferromagnetic layer is preferably made of a Ptxe2x80x94Mn alloy, an Xxe2x80x94Mn alloy, wherein X is at least one element selected from Pd, Ir, Rh, and Ru, or a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, wherein Xxe2x80x2 is at least one element selected from Pd, Ir, Rh, Ru, Au, and Ag.
In a further aspect, the present invention provides a magnetoresistive element which includes a multilayer film including a magnetoresistive layer, a nonmagnetic layer, and a soft magnetic layer laminated in this order; a pair of bias layers formed on both sides of the multilayer film; and a pair of electrode layers formed on the bias layers. In this magnetoresistive element, an insulating layer is formed on the multilayer film between the electrode layers, and the electrode layers formed on both sides of the multilayer film are in contact with the sides of the insulating layer directly or through the interposition of another layer.
In the invented magnetoresistive element, the height of an upper edge and/or a lower edge of a magnetic interface between the multilayer film and the bias layer in a medium moving direction is preferably equal to the height of an upper side and/or a lower side of the free magnetic layer or the magnetoresistive layer in a medium moving direction.
The bias layer is magnetically connected with a side of the multilayer film in a track width direction directly or through the interposition of another layer such as an underlayer. The bias layer serves to align the magnetization vector in the free magnetic layer or of the magnetoresistive layer in a fixed direction. Accordingly, the bias layer has only to be magnetically connected with the free magnetic layer or the magnetoresistive layer alone. More preferably, the bias layer is not magnetically connected with the pinned magnetic layer to thereby suppress a magnetic field generated from the bias layer from affecting the magnetization vector in the pinned magnetic layer.
Preferably, the multilayer film includes a sensing region at the center and dead zones on both sides of the sensing region, the sensing region has a satisfactory reproducing sensitivity and is capable of substantially exhibiting a magnetoresistive effect, and the dead zones have a poor reproducing sensitivity and are not capable of substantially exhibiting a magnetoresistive effect, and the electrode layers formed on both sides of the multilayer film extend over the dead zones in the multilayer film.
In the conventional magnetoresistive element, the magnetization vector in the pinned magnetic layer is put into a single magnetic domain state and is fixed in a direction (the Y direction in FIG. 14) out of an opposite face of the recording medium, whereas the hard bias layers magnetized in a track width direction (the X direction in FIG. 14) are formed on both sides of the pinned magnetic layer. By this configuration, the magnetization vectors in the pinned magnetic layer at both ends are put into the track width direction by the effect of a bias magnetic field from the hard bias layers.
Specifically, by effect of magnetization of the hard bias layers in the track width direction, the magnetization vector in the fee magnetic layer which is put into a single magnetic domain state in the track width direction is not orthogonal to the magnetization vector in the pinned magnetic layer particularly in the vicinity of the side ends of the multilayer film. The reproducing sensitivity is thus decreased and an output waveform with a satisfactory symmetry cannot be obtained.
In addition, the magnetization vector in the free magnetic layer in the vicinity of its side end is significantly affected by a strong magnetization from the hard bias layer, and is apt to be fixed, and the magnetization becomes hard to vary with an external magnetic field.
Accordingly, dead zones having a poor reproducing sensitivity are formed in the vicinity of the side ends of the multilayer film, and, a central region of the multilayer film other than the dead zones constitutes a sensing region which substantially contributes reproduction of a recorded magnetic field and exhibits a magnetoresistive effect (FIG. 14).
According to the present invention, the electrode layers formed on both sides of the multilayer film extend over the dead zones of the multilayer film, and the sensing current from the electrode layers is resistant to flow into the hard bias layer. Accordingly, an increased proportion of the sensing current can flow directly into the multilayer film without the interposition of the hard bias layer, and the hard bias layer is in contact with the electrode layers with an increased area to reduce a direct current resistance (DCR) to thereby improve the reproducing characteristics.
Such electrode layers extending over the dead zone can prevent the sensing current from flowing into the dead zone and from producing noises.
The sensing region of the multilayer film may be defined as a region which yields an output of 50% or more of the maximum read output, and the dead zones of the multilayer film may be defined as regions which are on both sides of the sensing region and yield an output less than 50% of the maximum read output, as determined by allowing a magnetoresistive element including electrode layers formed only on both sides of the multilayer film to scan on a microtrack with a recorded signal in a track width direction.
When the protective layer is formed on a top surface of the multilayer film, it is preferably formed on the multilayer film in a portion which is not joined with the electrode layers.
Preferably, the sensing region of the multilayer film has an equal width to an optical read track width O-Tw.
The width of each of the electrode layers in a portion extending over the multilayer film is preferably more than 0 xcexcm and equal to or less than 0.08 xcexcm, and more preferably equal to or more than 0.05 xcexcm and equal to or less than 0.08 xcexcm.
The invented magnetoresistive element is preferably manufactured by the following process so that a side of the multilayer film becomes in parallel with a side of the insulating layer.
In yet another aspect, the present invention provides a process for manufacturing a magnetoresistive element which includes a step of forming a multilayer film on a substrate, the multilayer film exhibits a magnetoresistive effect; a step of forming an insulating layer on the multilayer film; a step of forming a resist layer for lift-off on the insulating layer; a step of forming bias layers on both sides of the multilayer film and magnetizing the formed bias layers in a track width direction; a step of forming electrode layers from an oblique direction with respect to the multilayer film, where each of the electrode layers is formed in contact with a side of the insulating layer directly or through the interposition of another layer, and the insulating layer underlies the resist layer; and a step of removing the resist layer from above the insulating layer.
The process preferably further includes a step of forming an antioxidant protective layer on a top surface of the multilayer film in the step of forming the multilayer film exhibiting a magnetoresistive effect on the substrate.
In the step of forming electrode layers, a surface of the protective layer or a surface of the multilayer film other than the protective layer forms an angle of preferably 60 degrees or more, and more preferably 90 degrees or more, with respect to front end faces of the electrode layers extending over dead zones of the multilayer film.
In the step of forming the resist layer for lift-off on the insulating layer, the resist layer preferably has an incision at the bottom facing a region of the multilayer film, which region is to be a dead zone being previously determined by microtrack profiling and the resist layer is formed on the insulating layer in a region above a sensing region of the multilayer film, and the process preferably further includes a step of etching to thereby remove the insulating layer even inside the incision formed at the bottom of the resist layer. By this configuration, the electrode layers can extend over the dead zones of the multilayer film in the step of forming the electrode layers.
In this connection, the sensing region of the multilayer film determined by microtrack profiling may be defined as a region which yields an output of 50% or more of the maximum read output, and the dead zones of the multilayer film may be defined as regions which are on both sides of the sensing region and yield an output less than 50% of the maximum read output, as determined by allowing a magnetoresistive element including electrode layers formed only on both sides of the multilayer film to scan on a microtrack with a recorded signal in a track width direction.
When the antioxidant protective layer is formed on a top surface of the multilayer film in the step of forming the multilayer film exhibiting a magnetoresistive effect on the substrate, the process may preferably further include a step of removing a region of the protective layer being not covered by the insulating layer to expose a layer underlying the protective layer subsequent to the step of etching to thereby remove the insulating layer even inside the incision formed at the bottom of the resist layer.
In the invented process, preferably, the substrate with the formed multilayer film is placed in a direction perpendicular to a target having a composition of the bias layers, and the bias layers are formed on both sides of the multilayer film by at least one sputtering process selected from ion beam sputtering, long-throw sputtering and collimation sputtering, and subsequently, the substrate with the formed multilayer film is placed in an oblique direction with respect to a target having a composition of the electrode layers or the target is placed in an oblique direction with respect to the substrate, and films of the electrode layers are formed on the bias layer even inside an incision formed at the bottom of the resist layer on the multilayer film, by at least one sputtering process selected from ion beam sputtering, long-throw sputtering and collimation sputtering.
The multilayer film preferably includes at least one each of an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic layer, and a free magnetic layer, or includes a free magnetic layer, and combinations of a nonmagnetic layer, a pinned magnetic layer, and an antiferromagnetic layer on and under the free magnetic layer, or includes a magnetoresistive layer, a nonmagnetic layer, and a soft magnetic layer laminated in this order.
The free magnetic layer is preferably formed so as to include plural soft magnetic thin films having different magnetic moments and being laminated with each other through the interposition of a nonmagnetic material layer, and the free magnetic layer is preferably in a ferrimagnetic state where the magnetization vectors of a pair of the soft magnetic thin films being adjacent to each other through the interposition of the nonmagnetic material layer are in parallel with and opposite to each other.
When the free magnetic layer is formed so as to include plural soft magnetic thin films having different magnetic moments and being laminated with each other through the interposition of a nonmagnetic material layer, a magnetic interface between the multilayer film and the bias layer is preferably allowed to overlay a side of only one soft magnetic thin film, of sides of the plural soft magnetic thin films constituting the free magnetic layer, in the step of forming the bias layers.
Preferably, the pinned magnetic layer is formed so as to include plural soft magnetic thin films having different magnetic moments and being laminated with each other through the interposition of a nonmagnetic material layer, and the pinned magnetic layer is in a ferrimagnetic state where the magnetization vectors in a pair of the soft magnetic thin films adjacent to each other through the interposition of the nonmagnetic material layer are in parallel with and opposite to each other.
The nonmagnetic material layer is preferably made of one metal or an alloy of two or more metals selected from Ru, Rh, Ir, Cr, Re, and Cu.
In the step of forming the bias layers, the height of an upper edge and/or a lower edge of a magnetic interface between the multilayer film and the bias layer in a medium moving direction is preferably set at equal to the height of an upper side and/or a lower side of the free magnetic layer or the magnetoresistive layer in a medium moving direction.
According to the present invention, the antiferromagnetic layer is preferably made of a Ptxe2x80x94Mn alloy. Alternatively, the antiferromagnetic layer may be made of an Xxe2x80x94Mn alloy, wherein X is at least one element selected from Pd, Ir, Rh, and Ru, or may be made of a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, wherein Xxe2x80x2 is at least one element selected from Pd, Ir, Rh, Ru, Au, and Ag.
In the step of etching to thereby remove the insulating layer even inside the incision formed at the bottom of the resist layer, the insulating layer may be etched in such a manner that the sides of the insulating layer are kept in parallel with the sides of the multilayer film.
If the width of the top surface of the multilayer composed of, for example, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic layer, and a free magnetic layer laminated in this order is defined as a track width Tw, the overall multilayer film does not actually exhibit a magnetoresistive effect. The central region of the multilayer film alone has a satisfactory reproducing sensitivity, and substantially the central region alone can exhibit the magnetoresistive effect. The region of the multilayer film having a satisfactory reproducing sensitivity is called as a sensing region and the region having a poor reproducing sensitivity is called as a dead zone. The sensing region and dead zones occupying the multilayer film are determined according to microtrack profiling technique. The microtrack profiling technique will be described below, with reference to FIG. 13.
Initially, a conventional magnetoresistive element (FIG. 14) is formed on a substrate, which magnetoresistive element includes a multilayer film exhibiting a magnetoresistive effect, hard bias layers formed on both sides of the multilayer film, and electrode layers formed on the hard bias layers, as shown in FIG. 13. The electrode layers are formed only on both sides of the multilayer film.
Next, the width A of a top surface of the multilayer film in a portion not covered by the electrode layers is determined with an optical microscope. The width A is defined as a track width Tw which is determined by an optical technique (hereinafter referred to as xe2x80x9coptical read track width O-Twxe2x80x9d).
A signal is then recorded on a microtrack on a recording medium, and the magnetoresistive element is allowed to scan on the microtrack in the track width direction to thereby determine the relation between the width A of the multilayer film and a read output. Alternatively, the recording medium with the formed microtrack is allowed to scan on the magnetoresistive element in the track width direction to thereby determine the relation between the width A of the multilayer film and a read output. The result thereof is shown in a lower side of FIG. 13.
The result shows that the read output is high around the center of the multilayer film and is low in the vicinity of the periphery of the multilayer film, indicating that the central region of the multilayer film exhibits a satisfactory magnetoresistive effect to contribute a reproducing function, whereas the peripheral region thereof exhibits a deteriorated magnetoresistive effect and has a low read output and exhibits a decreased reproducing function.
In the present invention, a region having a width B on a top surface of the multilayer film, which yields an output of 50% or more of the maximum read output is defined as a sensing region, and a region having a width C on a top surface of the multilayer film, which yields an output less than 50% of the maximum read output is defined as a dead zone.
In the dead zone, the reproducing function does not effectively act and serves only to increase a direct current resistance (DCR). According to the present invention, the electrode layers therefore extend even over the dead zone to thereby increase junction areas between the hard bias layers and the electrode layers formed on both sides of the multilayer film and to facilitate a sensing current from the electrode layers to flow into the multilayer film without the interposition of the hard bias layers. The direct current resistance can therefore be reduced to thereby improve the reproducing characteristics.